2 phones, same line AT&T

I currently have and love the Galaxy S4 GPE. I'm toying with getting the Sony Xperia Z2 as well. Is it just a matter of swapping the SIM card between to 2 phones or is it more involved than that? I know that I can't use BOTH phones at the same time, but I'd like to go back and forth between the 2 phones until such time I can decide which one to keep. Thanks all.

ID4me is an internet service that enables its users to log in to many different internet services with one account. This is also known as "single sign on".

Unlike existing global single sign on solutions like the ones from Google or Facebook, ID4me does not track and analyze the internet surfing habits of its users. ID4me will make sure that the surfing habits stay secret.

Also, ID4me does not belong to an enterprise. It is an open standard that is maintained by a nonprofit organization. Anyone who wants to can participate. This way the users can chose freely between different ID4me providers and can also change the provider anytime.